White Fungus on Trees

Spanish moss is a whitish-colored, hanging lichen.

Several white or whitish fungi attack trees or simply live on or near them. Healthy trees are less susceptible to many forms of dangerous fungi; therefore, proper watering, fertilization and pruning practices can help prevent infection. Older trees and those with wounds are much more susceptible than other trees to various fungal attacks.

Powdery Mildew

Powdery mildew forms a white to silvery, powderlike fungus on the tops and bottoms of leaves. Although many types of powdery mildew exist, they all produce the powdery symptoms. Most types of the fungus are host-specific. This fungus thrives in certain environmental conditions; shaded, crowded locations with poor air circulation increase the chances and spread of this disease. Avoiding overhead watering and thinning tree branches to improve air circulation can help prevent the disease and stop it from spreading. Removing and destroying infected branches also helps to prevent the spread of powdery mildew.

Armillaria

Armillaria fungi are responsible for deaths of hardwood trees, forest stands, fruit trees and woody shrubs throughout the world's temperate and tropical regions. In some cases, white to yellowish, fan-shaped mushrooms appear on trees or between their bark and wood. A white, spongelike rot of the wood is a common symptom when mushrooms aren't present. Trees infected with one of these fungi often shows leaf discoloration, stunted growth and branch die-back.

Lichens

Lichens tend to grow on healthy, living trees, unlike many other fungi. Three kinds of lichens occur on trees: those that form crustlike coverings on trees; those that are more leaflike in nature; and those that hang, are erect or bushlike. Some lichens cover a tree's trunk and branches in a white, scaly crust. Spanish moss is a hanging lichen that commonly occurs in California's "fog belt" near the coast. Because lichens rarely cause harm, treatment for them often is unnecessary. You can, however, scrub off lichens or spray affected areas to remove the growths.

White Mushroom Growths

Many fungi that attack trees have a whitish color and are often noticed when mushrooms appear. Common split gill (Schizophyllum commune), oyster mushrooms (Pleurotus ostreatus) and hairy turkey tail (Trametes hirsuta) all form white mushrooms when they infect a tree. Trees infected may include alder, birch, chestnut, elm, walnut, spruce and willow. All of these fungi cause white rot much like Armillaria. White rot makes wood soft, moist and stringy to the touch.